Refrigeration system defrost control



Feb. 23, 1965 D. B. DIBBLE ETAL REFRIGERATION SYSTEM DEFROST CONTROL Filed Sept. 26, 1965 I3 FIG. I

I I I I I I I I I I I I I INVENTOR. DAVID B. DIBBLE.

FIG. 2

HARRY T. HALE.

ATTORNEY.

United States Patent 3,17 0,305 REFRIGERATION SYSTEM DEFROST CONTROL David B. Dibble, North Syracuse, and Harry T. Hale, Bridgeport, N.Y., assignors to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware 1 Filed Sept. 26, 1963, Ser. No. 311,841

5 Claims. (Cl. 62-155) This invention relates to a control arrangement for refrigeration systems, and more particularly to a control arrangement for refrigeration systems operable to selectively heat and cool.

Reverse cycle refrigeration systems, commonly referred to as heat pumps, may include an arrangement for defrosting the system outdoor coil'to restore system efficiency impaired through the formation of frost and ice thereon. While outdoor coil defrosting arrangements may assume various forms, a problem attendant with all forms is that of control, control of defrost initiation, duration, and termination in order that the outdoor coil may be effectively defrosted when necessary in the shortest possible time.

A usual method of defrosting the outdoor coil of a reverse cycle refrigeration system operating on the heating cycle is to revert to cooling cycle operation. By this arrangement, relatively hot gaseous refrigerant discharged from the system compressor is directed to the outdoor coil. Since operation of the system on the cooling cycle to effect removal of frost and ice from the outside coil not only interrupts the heating cycle but extracts heat from the area being conditioned, this method of defrosting the outside coil preferably is limited to as short a duration as possible. ln'systems relying on this method for defrosting the outdoor coil, the system, in response to a demand for heat, sometimes starts up on the cooling'or defrost cycle rather than on'the heating cycle. This 'is undesirable and unnecessary.

With the above discussion in mind, it is a principal object of the present inventionto provide a new and im-' proved defrost control arrangement for reverse cycle refrigeration systems.

It is a further object of the present inventionto provide a unique control arrangement and method of control for a reverse cycle refrigeration system effective to prevent, upon a demand for heat, energization of the system on the cooling or defrost cycle.

i a reverse cycle refrigeration system for selectively heating control for a reverse cycle refrigeration system effective to limit the duration of the defrost cycle to no more than a preset period of time. a

This invention relates to a control arrangement for a reverse cycle refrigeration system selectively energizable to heat and cool having compression means, an outdoor coil, refrigerant metering means, and an indoor coil connected in refrigerant flow relationship to cool, and means for reversing the flow of refrigerant through the indoor coil, refrigerant metering means, and outdoor coil to heat, comprising in combination means for defrosting the outdoor coil including first means actuated in response to a first outdoor coil condition to ready the defrosting means for operation and second means periodically actuated to ready the defrosting means for operation, the defrosting means being responsive to the simultaneous actuation of the first and second means to defrost the outdoor coil, the second means being adapted to. terminate outdoor coil defrost after a predetermined time interval, the first means intervening in response to a second outdoor coil condition to terminate outdoor coil defrost during the predetermined time interval, and means for regulating the defrosting means to prevent start up of the refrigeration system on'the defrost cycle.

The invention further relates to a method of operating and cooling an enclosure having means for removing frost accumulated on the system outdoor coil in which the steps consist in sensing outdoor coil conditions, periodically closing a switch for a relatively short interval, actuating the frost removing means on the occurrence of a predetermined outdoor coil condition during closure of the switch, bypassing the switch to maintain actuation of the frost removing means upon opening of the switch at the expiration of the relatively short interval, sensing operation of the system, and limiting actuation of the frost removing means to periods of system operation to prevent start-up ,of the system on the defrost cycle.

Other objects and features of the invention will be apparent from the ensuing specification and drawings in which: 7

FIGURE 1 is a diagrammatic view ofa reverse cycle refrigeration system forming the subject of this invention;

and

FIGURE 2 is a wiring diagram of an electric circuit for controlling the reverse cycle refrigeration system shown in FIGURE 1.

Referring more particularly to FIGURE 1 there is shown for the purpose of illustrating this invention an airto-air heat pump employing a refrigeration system operableunder the reverse cycle principle. In apparatus of this type a first heat transfer coil is disposed within the area to be conditioned by the heat pump and a second coil is located outside the area, usually in the ambient.

Compressor 1t) discharges relatively hot gaseous refrigerant through discharge line 11 to the reversing means 12, preferably, a four-way reversing valve, which is employed for the purpose of reversing refrigerant flow through a portion of the system in order to obtain the desired heating and cooling effects. From reversing means 12, controlled by the operation of the solenoid 13 in a manner later to be described, the hot gaseous refrigerant flows during cooling cycle operation through line.

14 to outdoor heat exchange coil 15 wherein condensation of the gaseous refrigerant occurs as ambient air is passed over the surface of outdoor coil.15 by fan 20.

The condensed liquid refrigerant flows from coil 15 through suitable expansion means 16 to indoor heat exchange coil 17, serving as an evaporator during the cooling cycle. able to permit flow in the direction shown by the solid line arrow provides a path for refrigerant flow around expansion means 28. Expansion means 16 provides the requisite pressure drop between the heat exchange coils in the refrigeration system during cooling cycle operation;

In indoor heat exchange coil 17, refrigenant is vaporized as heat is extracted from the stream of air delivered over the indoor coil by fan 21. Vaporous refrigerant so formed flows through line 18 to reversing valve 12 from whence the refrigerant flows through suction line 19 back to compressor 10 to complete the refrigerant flow cycle.

l Each of the fans 20 and 21 may be driven by suitable drive mechanism, for example, electric motors 25 and 26 respectively.

To heat the area to be treated the reversing valve 12 is actuated to place line 18 in communication with discharge line 11. Under these circumstances heat from the hot gaseous refrigerant flowing into coil 17 is rejected to the air within the area to be treated. The rejection of heat from the refrigenant converts the gaseous refrigerant to liquid refrigerant which flows through expansion means 28 to outdoor coil 15, which now functions as an,

evaporator. Line 29 having check valve control 31 therein operable to permit flow of refrigerant in the direction shown by the dotted line arrow, provides a path for refrigerant flow around expansion means 16. The

Line 22 having check valve control 27 oper-- 3 vaporous refrigerant created in outdoor coil as a result of heat transfer between the refrigerant and the amblent air flows through reversing valve 12 into suction line 19 back to compressor 10. Expansion means 28 provides the requisite pressure drop between heat exchange coils in the refrigeration system during heating cycle operation.

A suitable low pressure cutout control 23 may be connected to the suction line 19 by suitable connecting means. Low pressure cutout control 23 actu ates a switch in the electrical circuit as will be later described.

As above noted the refrigeration system may be incapable of providing sufficient heat to the area to be treated during heating operation, especially when the heat pump is used in geographical areas which are subject to low outdoor ambient temperatures. An auxiliary heater 24 which consists of a suitable high resistance wire through which current is adapted to be selectively passed may be used to provide supplementary heat. Thus the air, heated to a certain degree by being induced through heat exchange coil 17 by fan 21, is further heated by being passed over resistance wire 24 which is energized upon closing of switch 100.

Referring to FIGURE 2 of the drawings, a suitable source of alternating current (not shown) is adapted to supply current via leads L1 and L2 to a primary control circuit. It will be understood of course that the system can operate on three-phase current, if it is suitably modified.

The motor for driving compressor 10 is energized when contacts 31 and 32 are closed. A contactor coil 35 for closing contacts 31 and 32 is provided.

A timer motor 37 for controlling energization of compressor motor 30 in response to a demand for heating or cooling is provided. Timer motor 37 drives suitable switch actuating mechanism, such as cam means operative to move timer switches 39 and 40 between the position shown in solid lines in FIGURE 2 of the drawings and that shown in dotted lines. Timer switch 39, when in the solid line position, connects contactor coil 35 in series with control switch 42 and switch 43 across leads L1 and L2. Timer switch 40, when in the solid line position, connects timer motor 37 in series with switch 49 across leads L1 and L2. A relay coil 50 for closing switch 43 and opening switch 49 is provided parallel to contactor coil 35 across leads L1 and L2 in series with control switch 42 and 43. Timer switch 39, when in the dotted line position, bypasses switch 43. Timer switch 40, when in the dotted line position, connects timing motor 37 in series with control switch 42 across leads L1 and L2.

Outdoor fan motor 25 is connected in series with a control switch 54 and defrost switch 55 across leads L1 and L2. Reversing valve solenoid 13 is connected across leads L1 and L2 in series with defrost switch 55 and reversing valve switch 56.

A defrost relay coil 58 adapted when energized to initiate defrosting of outdoor heat exchange coil 15 is connected in series with reversing valve switch 56 and defrost thermostat 60 across leads L1 and L2. Defrost timing motor 62 is connected in series across leads L1 and L2. The output shaft of defrost timing motor 62 is operatively connected by a suitable mechanism, such as cam means to a pair of defrost timer switches 64, 65 positioned in series with defrost relay coil 58 across leads L1 and L2. Defrost switch 70 parallels defrost timer switch 65 and is connected across leads L1 and L2 in series with defrost timer switch 64, defrost relay coil 58, defrost thermostat 60 and reversing valve switch 56. Defrost timer switch 65, normally open, and defrost switch 64, normally closed, are adapted to be periodically closed and opened respectively for a short duration in a predetermined sequence by the defrost timer motor driven mechanism in a manner to be more fullyexplained hereinafter. fan motor 26 is connected in series with indoor fanswitch 72 across leads L1 and L2.

Indoor The secondary control circuit may be electrically con nected to the primary control circuit by means of a: transformer 74.

mostat and a single-stage cooling thermostat.

ing valve relay 77. The second stage heating thermostat 79 is in series across outdoor thermostat 81 and resistance heater relay 82. When energized'relay 82' closes switch 160 to energize resistance heater 24, defrost relay switch 86 is disposed across heating thermostats 76 and 79. Switch 86 is closed during the defrost operation to energize the resistance heater 24 in a manner to be more fully explained hereinafter.

Also provided in the secondary control circuit are fan switch 87 which may be manually moved from an automatic position shown in solid line to a continuous operating position, shown in dotted line, and indoor fan relay 90 in series therewith.

A control relay 92 is in series across the secondary circuit with first'low' pressure switch 83 and cooling ther mostat 80. Low pressure switch 83 is normally closed.

, A circuitconnecting second low pressure switch 84 and defrost relay switch 85 in series parallels low pressure switch 83. Closure of switches 84 and 85 bypasses low pressure actuated switch 83. Low pressure switches 83 and 84 are opened and closed respectively in response to a predetermined suction pressure as sensed by low pressure cutout control 23.

Operation During cooling operation, the cooling thermostat 80 of the room thermostat 75 will close in response to a predetermined demand for cooling. Assuming that the indoor fan switch arm 87 is in the solid line position per mitting automatic operation of indoor fan 21, indoor fan relay 90 is energized to close indoor fan relay switch 72- in the primary control circuit thus energizing indoor fan motor 26. H

At the same time, control relay 92 isenergized t6 close control switches 42 and 54. A first c'ifc'iiit is air]? pleted via lead L1, normally closed defrost relai switch 55, control switch 54 and lead L2 to energize outdoor motor 25. A second circuit is completed via lead L1, control switch 42, timer switch 39, in dotted line position, and lead L2 to energize relay coil 50. Relay coil 50 close-s switch 43 and opens switch 49. A third circuit is com pleted via lead L1, control switch 42, timer switch 40 and lead L2 to energize the timer motor 37. After a predetermined interval, the switch actuating mechanism driven by timer motor 37 moves timer switches 39 and 49 to the solid line position.

Movement of timer switch 39 to the solid line positiori completes a circuit from lead L1 through control SWltCli 42 and switch 43 to lead L2 to energize contactor coil 35. Contactor coil 35 closes compressor control contacts 31 and 32 to energize the compressor motor 30 to drive compressor 10. Movement of timer switch 40 to the solid line position places timer motor 37 in series with switch 49, now open, to de-energize the timer motor.

During cooling operation, compressor 10 forwards high pressure vaporized refrigerant through reversing means 12 to line 14 and outdoor coil 15. Heat is extracted from the refrigerant by the air stream passing over coil 15, condensing the refrigerant. Condensed refrigerant passes through expansion means 16 to indoor coil 17 where the refrigerant is vaporized. The vaporized refrigerant returns to compressor Iii-through line 18, reversing means 12, and suction line 19.

Operation of the system on the heating cycle is initiated by closure of the first heating stage 76 of the room thermostat 75 in response to a demand for heating. Closure of first heating stage 76 energizes reversing valve relay 77 to close switches 56 and 85. Closure of reversing valve switch 56 completes a circuit from lead L1 through de-' Included in the secondary circuit is a room thermostat 75 comprising a two-stage heating ther- The firststage of a heating thermostat 76 is in series with revers-' Under the heating cycle of operation, refrigerant flows from indoor coil 17 through expansion means 28 to the outdoor coil 15. Heat rejected to the air passing over the indoor heat exchange coil warms the air being supplied to the area being conditioned. The hot vaporized refrigerant discharged from compressor is condensed in the indoor coil 17. The refrigerant vaporized in outdoor coil as a result of heat transfer between the refrigerant and the ambient air flows through reversing valve 12 into suction line 19 back to compressor 10.

During heating cycle operation, ambient conditions may be such that a coating of frost and/ or ice forms on outdoor coil 15. The defrost control means. depicted in FIG- URE 2 are operable to sense this accumulation of frost and/ or ice and,'ir1 response thereto, to temporarily reverse the system to cause the system to act on the defrost cycle to remove the accumulated frost and/ or ice.

Defrost timer motor 62 operates continuously. Periodically the switch actuating mechanism driven by the defrost timer motor closes defrost timer switch 65 for a brief interval. When defrost thermostat 68 senses a need for defrost and closes, a circuit is completed at the closure of defrost timer switch 65 via lead L1, defrost timer switches 64 and 65, defrost thermostat 60, reversing valve switch 56 and lead L2 to energize defrost relay 58. Defrost relay 58 closes defrost relay switch 70 to provide a holding circuit therefor and opens defrost relay switch 55 to de-energize reversing valve solenoid 13 and outdoor fan motor 25. At the same time, defrost relay 58 closes defrost relay switch 86 to permit energization of the auxiliary resistance heater 24 in a manner to be more fully explained hereinafter.

De-energization of reversing valve solenoid 13 permits reversing valve 12 to move to the position shown in FIG- URE l of the drawings whereby hot gaseous refrigerant from the compressor 10 is passed directly to outdoor coil 15 to remove frost and ice accumulated thereon.

As noted, during the defrost cycle, defrost relay switch 55 is open and outdoor fan motor 25 is accordingly deenergized. It is, however, desirable that the indoor fan be operative to provide a loaded evaporator whereby evaporator head pressure is maintained to insure the discharge of relatively hot gaseous refrigerant from the compressor. Continued operation of indoor fan 21 during the defrost cycle is assured in the following manner. The build-up of ice on outdoor coil 15 results in a drop in suction pressure. At a predetermined suction pressure, low pressure cutout 23 will open switch 83 and close switch 84. C10- sure of switch 84 maintains the circuit closed through indoor fan relay 90 to keep indoor fan control switch 72 closed and the indoor fan motor 26 operating.

Upon removal of the frost and ice from outdoor coil 15, defrost thermostat 60 opens. Additionally, normally closed timer switch 64 is opened for a brief interval by the defrost timer motor within a predetermined time after closure of timer switch 65. If defrost thermostat 60 opens within the predetermined time before timer switch 64 opens, defrost relay 58 is de-energized to terminate the defrost cycle in a manner to be described hereinafter. Should defrost thermostat 60-not open within the predetermined time before timer switch 64 is opened by the defrost timer motor 62, the opening of timer switch 64 de-ener'gizes defrost relay 58 to terminate the defrost cycle.- De-energiz'ation of defrost relay 58 upon the open mg of either defrost thermostat 60 or defrost timer switch 64, permits defrost relay switch 55 to close completing a circuit from lead L1 through switch 55 and reversing valve switch 56 to lead L2 to energize reversing valve solenoid 13 to move reversing valve 12 to the heating position. Ad

energize outdoor fan motor 25. V V I If during operation of the system on the heating cycle,

the demand for heat exceeds that capable of being supplied by the system alone, second stage heating thermostat 79 of indoor thermostat 75 will close at a predetermined temperature. Outdoor-thermostat 81 may be provided in series with the auxiliary heater relay 82 and thermostat 79. Outdoor thermostat 81 closes in response to a predetermined outdoor temperature. Closure of both second stage heating thermostat 79 and outdoor thermostat 81'energizes auxiliary heater relay 82 to close switch inergizing resistance heater 24 to provide supplementary eat.

The heretofore described defrost control arrangement causes the system to revert to cooling cycle operation. During cooling cycle operation, the indoor coil 17 functions as an evaporator. It is desirable during defrost cycle that indoor fan'21 be maintained in operation. However, the air blown over the indoor coil 17 during defrost cycle operation is chilled resulting in discomfort to occupants of the room being conditioned.

In the present heat pump control arrangement, air discharged into the room by the indoor fan 21 during the defrost cycle is tempered. This is efi'ected by maintaining the auxiliary heater relay 82 energized during defrost cycle operation. As noted heretofore, defrost relay switch 86 is closed on the defrost cycle. Closure of switch 86 completes a circuit through firststage heating thermostat 76 and defrost relay switch 86 to energize auxiliary heater relay 82 to close switch 100 and energize resistance heater 24.

By the novel control arrangement shown in FIGURE 2, the defrost control circuitry is made dependent for its energization upon actuation of the system reversing relay. This dependency is effected through the placement of reversing valve switch 56 in series with the energizing circuits for defrost relay 55 and reversing valve solenoid 13. By this arrangement, should overlapping closure of the defrost timer motor-driven switch 64 and defrost thermostat 60 occur while the unit is shut down, the unit will not, upon closure of the first stage heating thermostat 76, start up on the defrost or cooling cycle. In this arrangement, initiation of the defrost cycle will not take place until such time as the defrost timer switch 65 closes.

While we have described a preferred embodiment of the invention, it will be understood that the invention is not limited thereto, since it may be otherwise embodied in the scope of the following claims.

We claim:

1. In a control arrangement for a reverse cycle refrigeration system selectively energizable to heat and cool, having compression means, an outdoor coil, refrigerant metering means, and an indoor coil connected in refrigerant flow relationship to cool, and means for reversing the flow of refrigerant through the indoor coil, said refrigerant metering means, and said outdoor coil to heat, the combination comprising control means for regulating said reversing means for defrosting the outdoor coil including first means operable in response to a first outdoor coil condition to ready said defrosting control means for operation, and second means periodically operable to ready said defrosting control means for operation, said defrosting control means being responsive to the substantially simultaneous actuation of the first and second means to defrost the outdoor coil, said second means being adapted to terminate outdoor coil defrost after a predetermine time interval, said first means intervening in response to a second outdoor coil condition to terminate outdoor coil defrost during said predetermined time inter-.

val, and condition responsive meansfor regulating said defrost control means toprevent start-up of the defrost cycle during the remainder of the predetermined time interval.

2. The control arrangement according to claim 1 including circuit means for energizing said defrosting control means having first and second switches, said first means being operable upon actuation to close said first switch, said second means being operable upon actuation .to close said second switch, said condition responsive means including switch means for interrupting said circuit means in response to de-energization of the refrigeration system.

. 3. The control arrangement according to claim 2 including circuit means for energizing said reversing means in series with said switch means.

4. In a refrigeration system for conditioning an enclosure, the combination of compression means, an out door coil, refrigerant metering means, and an indoor coil connected in refrigerant flow relationship operable upon energization of the compression means to cool, and reversing means efiective when energized to connect the compression means, said indoor coil, said refrigerant metering means, and said outdoor coil in refrigerant flow relationship operable upon energization of the compression means to heat, fan means operable to pass air over the indoor coil during operation of the system on the cooling and'heating cycle, and a control arrangement comprising a first circuit for energizing said reversing means, switch means in said first circuit for controlling energize,- tion or" said reversing means in response to enclosure conditions, said switch means being adapted to close in response to a predetermined enclosure condition to complete said first circuit to energize said reversing means, a second circuit connected in series with said switch means, said second circuit having a first switch periodically closed and a second switch closed in response to a predetermined system condition, said second cirrcuit being operable to closure of said first and second switches to interrupt said first circuit to de-energize said reversing means to defrost the outdoor coil.

5. The control arrangement as recited in claim 4 in which'said second circuit includes a third switch opened a predetermined time following the closure of said second switch to interrupt said second cirrcuit to terminate outdoor coil defrost.

References Cited by the Examiner UNITED STATES PATENTS 2,143,687 1/39 Crago 62155 2,847,833 8/58 Merrick 62-l55 ROBERT A. OLEARY, Primary Examiner.

WILLIAM J. WYE, Examiner. 

1. IN A CONTROL ARRANGEMENT FOR A REVERSE CYCLE REFRIGERATION SYSTEM SELECTIVELY ENERGIZABLE TO HEAT AND COOL, HAVING COMPRESSION MEANS, AN OUTDOOR COIL, REFRIGERANT METERING MEANS, AND AN INDOOR COIL CONNECTED IN REFRIGERANT FLOW RELATIONSHIP TO COOL, AND MEANS FOR REVERSING THE FLOW OF REFRIGERANT THROUGH THE INDOOR COIL, SAID REFRIGERANT METERING MEANS, AND SAID OUTDOOR COIL INTHE COMBINATION COMPRISING CONTROL MEANS FOR REGULATING SAID REVERSING MEANS FOR DEFROSTING THE OUTDOOR COIL INCLUDING FIRST MEANS OPERABLE IN RESPONSE TO A FIRST OUTDOOR COIL CONDITION TO READY SAID DEFROSTING CONTROL MEANS FOR OPERATION, AND SECOND MEANS PERIODICALLY OPERABLE TO READY SAID DEFROSTING CONTROL MEANS FOR OPERATION, SAID DEFROSTING CONTROL MEANS BEING RESPONSIVE TO THE SUBSTANTIALLY SIMULTANEOUS ACTUATION OF THE FIRST AND SECOND MEANS TO DEFROST THE OUTDOOR COIL, SAID SECOND MEANS BEING ADAPTED TO TERMINATE OUTDOOR COIL DEFROST AFTER A PREDETERMINE TIME INTERVAL, SAID FIRST MEANS INTERVENING IN RESPONSE TO A SECOND OUTDOOR COIL CONDITION TO TERMINATE OUTDOOR COIL DEFROST DURING SAID PREDETERMINED TIME INTERVAL, AND CONDITION RESPONSE MEANS FOR REGULATING SAID DEFROST CONTROL MEANS TO PREVENT START-UP OF THE DEFROST CYCLE DURING THE REMAINDER OF THE PREDETERMINED TIME INTERVAL. 